QIQG 2025

Jun 23, 2025, 8:00 a.m. → Jun 27, 2025, 5:00 p.m. America/Toronto

PI/1-100 - Theatre (Perimeter Institute for Theoretical Physics)

 

QIQG 2025: Quantum Information in Quantum Gravity

 

QIQG 2025: Quantum Information In Quantum Gravity will unite researchers working at the intersection of quantum information theory and quantum gravity, to exchange insights and showcase recent developments bridging these fields. As part of the celebrations of Perimeter’s 25th anniversary, we will also feature vision talks by world-leading experts exploring pivotal and emerging themes at the nexus of quantum information and quantum gravity. Our program will span topics such as:

 

• Algebraic approaches to field theory and gravity
• Observers, quantum reference frames, and relational observables
• Quantum focussing and the Generalized Second Law
• SYK and its double-scaled limit
• The quantum information theoretic structure of spacetime
• Edge modes and entanglement entropy across subregions
• The role of complexity in field theory and gravity
• The black-hole information puzzle and related issues
• Quantum error-correcting codes in quantum field theory and quantum gravity
• Quantum cryptography and its implications for gravity
• Gravitational wormholes and their information-theoretic implications
• Chaos and thermalization in many-body systems and their realization in quantum gravity
• Holographic cosmology and de Sitter space

 

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Scientific Organizers

Luca Ciambelli (Perimeter Institute)
Rob Myers (Perimeter Institute)
Chris Waddell (Perimeter Institute)
Beni Yoshida (Perimeter Institute)

Mon, June 23

8:30 a.m. Registration

1 Opening Remarks

Speakers: Marcela Carena (Perimeter Institute for Theoretical Physics), Emily Petroff (Perimeter Institute for Theoretical Physics), Chris Waddell (Perimeter Institute for Theoretical Physics)

2 The Holography of de Sitter Space: DSSYK as a concrete example (Vision Talk)

I will discuss the holographic principle as applied to de Sitter space and the concrete example of double-scaled SYK at infinite temperature.

Speaker: Lenny Susskind (Stanford University)

10:50 a.m. Break

3 Chaos and the Emergence of the Cosmological Horizon

We construct algebras of diff-invariant observables in a global de Sitter universe with two observers and a free scalar QFT in two dimensions. In the limit when the observers have infinite mass and are localized along geodesics at the North and South poles, it was shown in previous work (CLPW) that their algebras are mutually commuting type II_1 factors. Away from this limit, we show that the algebras fail to commute and that they are type I non-factors. Physically, this is because the observers' trajectories are uncertain and state-dependent, and they may come into causal contact. We compute out-of-time-ordered correlators along an observer's worldline, and observe a Lyapunov exponent given by 4πβ_dS, as a result of observer recoil and de Sitter expansion. This should be contrasted with results from AdS gravity, and exceeds the chaos bound associated with the de Sitter temperature by a factor of two. We also discuss how the cosmological horizon emerges in the large mass limit and comment on implications for de Sitter holography.

Speaker: David Kolchmeyer (MIT)

4 Operator Algebras and Third Quantization

In quantum gravity, the gravitational path integral involves a sum over topologies, representing the joining and splitting of multiple universes. To account for topology change, one is led to allow the creation and annihilation of both closed and open universes in a framework often called third quantization or universe field theory. We argue that since topology change in gravity is a rare event, its contribution to late-time physics should be universally governed by a Poisson distribution. In the Fock space of closed baby universes, this Poisson distribution corresponds to the statistics of the number operator in a coherent state, whereas allowing for the creation of asymptotic open universes calls for a non-commutative generalization of a Poisson process. We propose such an operator algebraic framework, called Poissonization, which takes as input the observable algebra and a (unnormalized) state of a quantum system and outputs a von Neumann algebra represented on its symmetric Fock space. Physically, our construction is a generalization of the coherent state vacua of bipartite quantum systems.

Speaker: Nima Lashkari (Purdue University West Lafayette)

12:30 p.m. Group Photo

12:40 p.m. Lunch

2:00 p.m. Free Time

5 Swing Surfaces in AdS/CFT

The entanglement entropy for regions in a BMS field theory living at null infinity has been proposed to be holographically dual to certain ‘swing surfaces’ in flat space. We lift this construction to AdS/CFT and revisit both bulk and boundary aspects of this proposal.

Speaker: Sabrina Pasterski (Perimeter Institute for Theoretical Physics)

6 An Emergent Area Operator in 2d CFT

The Ryu-Takayanagi formula implies that the entropy, a non-linear function of the state, is an observable in the semiclassical limit. This is a general phenomenon in a class of quantum error-correcting codes (QECC), but few specific area operators in the boundary CFT. In this work, I define a specific code in a holographic 2d CFT that includes all thermofield double states with arbitrary amounts of time evolution, but no bulk local degrees of freedom. While the naive area operator vanishes, it is possible to write down an area operator for appropriately classical states; the answer matches with previous results obtained from bulk considerations. Interestingly, this area operator involves an explicit coarse-graining. This suggests a construction for a non-isometric holographic map for these states.

Speaker: Ronak Soni (Chennai Mathematical Institute)

3:30 p.m. Break

7 Gravity As An Oracle (Vision Talk)

Our search for a quantum theory of gravity is aided by a unique and perplexing feature of the classical theory: General Relativity “knows” about its own quantum states (the entropy of a black hole), and about those of all matter (via the Quantum Focusing Conjecture). The results we are able to extract from classical gravity are inherently non-perturbative and increasingly sophisticated. Recent breakthroughs include a derivation of the entropy of Hawking radiation, a computation of the exact integer number of states of some black holes, a proof of the QFC, and the construction of gravitational holograms in general spacetimes. The nature of the oracle, and its full power, remain unknown.

Speaker: Raphael Bousso (University of California, Berkeley)

5:00 p.m. Welcome Reception

Tue, June 24

8 Vacuogenesis (Vision Talk)

I will offer perspectives on the creation of degrees of freedom, relational observables, probability, observable algebras, and gravity.

Speaker: Ted Jacobson (University of Maryland, College Park)

10:50 a.m. Break

9 Randomizing excitations of half-BPS states gives near-extremal black holes

I will discuss a concrete realization in N=4 SYM of the mechanism of cryptographic censorship: that sufficiently random time evolution in a holographic CFT incurs an event horizon in the bulk dual. I will show that perturbing half-BPS states by randomly distributing a large number of defects on them corresponds in the gravitational dual to exciting an extremal (horizonless) black hole to near-extremality. This random distribution of defects corresponds to acting with a typical random isometry on the half-BPS subspace. This allows us to interpret this process in the field theory as an extension of cryptographic censorship.

Speaker: Evita Verheijden (MIT)

10 Absolute Entropy and the Observer's No-Boundary State

I will discuss the algebra of observables accessible to an observer in a generic closed universe and the role of the no-boundary density matrix in defining entropy.

Speaker: Jonah Kudler-Flam (Institute for Advanced Study)

12:30 p.m. Lunch

2:00 p.m. Free Time

11 Towards an information theory of scrambling

A scrambling unitary never destroys information according to quantum information/Shannon theory. However, this framework alone doesn’t capture the fact that scrambled information can be effectively inaccessible. This limitation points to the need for a new kind of information theory—one that quantifies how much information is scrambled, rather than how much is lost to noise. To address this, we propose introducing a new family of entropies into physics: free entropy. Unlike conventional quantum entropies, which are extensive under tensor independence, free entropy has the defining feature of extensivity under freeness—the appropriate notion of independence pertaining to quantum scrambling.

I will present a preliminary result showing how free entropy naturally arises in a variant of Schumacher compression, providing it with an operational interpretation as the quantum minimum description length of quantum states. I will sketch how this interpretation extends to observables and unitaries, allowing free entropy to capture an operational aspect of quantum scrambling. Finally, I will highlight striking parallels between free entropy and von Neumann entropy, suggesting that free entropy may form the foundation of a new, complementary information theory.

Speaker: Jinzhao Wang (Stanford University)

12 The free mutual information as a measure of quantum chaos

I will introduce a quantity from noncommutative probability theory called the free mutual information, and discuss how it can be used as a new diagnostic of quantum many-body chaos. This quantity captures a notion of the spreading of the operator in the abstract space of all possible time-evolved operators, rather than the more familiar notion of spreading in the physical space of degrees of freedom. I will discuss a precise relation between the free mutual information and the higher-point out-of-time-ordered correlators which applies in any system. I will further discuss the behaviour of the free mutual information in a few representative models of chaotic systems, and how it is sensitive to features of the dynamics beyond those captured by the four-point out-of-time-ordered correlator.

Speaker: Shreya Vardhan (Stanford University)

3:30 p.m. Break

13 Visions of RealTime: The Lorentz-signature gravitational path integral for fun and profit (Vision Talk)

The Euclidean gravitational action is unbounded below. As a result, even at the effective field theory level, the gravitational path integral cannot be formulated as an integral over real Euclidean geometries. I therefore review recent efforts to formulate the path integral directly in Lorentz-signature in a manner that allows general topology-changing transitions. I will also describe how this formulation resolves certain puzzles associated with computing the density of states for nearly-extremal black holes.

(VIRTUAL TALK)

Speaker: Donald Marolf (UC Santa Barbara)

6:00 p.m. Banquet

Wed, June 25

14 Holographic models of big bang cosmology (Vision Talk)

I will describe various constructions of cosmological spacetimes with big bangs using the tools of holography. I will point out features that appear to be common to holographic models of cosmology and discuss general questions that these models might be used to understand.

Speaker: Mark Van Raamsdonk (University of British Columbia)

10:50 a.m. Break

15 Quantum Field Theory on the edge

In this talk I will report on recent developments concerning quantization of field theories on manifolds with boundary. In perturbative AQFT this can be realized using a version of BV-BFV formalism, following the program outlined by Mnev, Cattaneo and Reshetikin. I will also argue that in pAQFT one always implicitly introduces boundaries and that there are good conceptual reasons to do so. This is joint work with Michele Schiavina.

Speaker: Katarzyna Rejzner (University of York)

16 The gravitational path integral from an observer's point of view

One of the fundamental problems in quantum gravity is to describe the experience of a gravitating observer in generic spacetimes. In this talk, I will describe a framework within which we can analyze non-perturbative physics relative to an observer using the gravitational path integral. We apply our proposal to an observer that lives in a closed universe and one that falls behind a black hole horizon. We find that the Hilbert space that describes the experience of the observer is much larger than the Hilbert space in the absence of an observer. In the case of closed universes, the Hilbert space is not one-dimensional, as calculations in the absence of the observer suggest. Rather, its dimension scales exponentially in 1/G_N. Similarly, from an observer's perspective, the dimension of the Hilbert space in a two-sided black hole is increased and this drastically changes what an observer sees when falling past the horizon of a black hole at late times.

Speaker: Luca Iliesiu (University of California, Berkeley)

17 Flash Talks - 1 min, 1 slide

1:00 p.m. Lunch

2:00 p.m. Free Time

2:30 p.m. Poster Session

7:00 p.m. Public Lecture (Ticket Required)

Thu, June 26

18 Holography and Pseudo (Entanglement) Entropy (Vision Talk)

The holographic calculation of entanglement entropy implies that space coordinate in gravity may emerge from quantum entanglement. The next key question will be to understand how time coordinate may emerge from quantum information. After we review recent developments of pseudo entropy, which is a generalization of entanglement entropy, and its holographic calculation, we will point out that this quantity looks like a useful starting point to understand the emergence of time, by studying explicit examples of time-like entanglement entropy, traversable wormhole and dS/CFT. In the final short time, we would also like to briefly discuss how much the AdS/CFT is efficient as a quantum computer, where the notion of pseudo entanglement in the context of pseudo random states, plays an important role.

Speaker: Tadashi Takayanagi (Yukawa Institute for Theoretical Physics)

10:50 a.m. Break

19 Chaos in deformed SYK models

The SYK model has attracted significant interest for its maximal chaos, connections to two-dimensional holography, and relevance to strange metals.
Two signatures of chaos in this model are out-of-time-ordered correlators (OTOCs) and Krylov complexity, both exhibiting early-time exponential behaviours characterized by the Lyapunov and Krylov exponents, respectively. In this talk, I explore these quantities in a class of relevant deformations of the SYK model, including flows which interpolate between two regions of near-maximal chaos and flows that lead to a nearly-integrable behaviour at low temperatures. I present both analytic and numerical results showing that the Krylov exponent consistently upper-bounds the Lyapunov exponent. Notably, while the Lyapunov exponent varies non-monotonically with temperature, the Krylov exponent remains smooth and monotonic, showing no clear signatures across chaotic transitions. This challenges the effectiveness of Krylov complexity as a diagnostic of chaos in quantum mechanical systems. I will also comment on the potential relevance of SYK flows for de Sitter holography and on connections to other recent works.

Speaker: Shira Chapman (Ben Gurion University)

20 Area and time

A diffeomorphism-invariant definition of physical subsystems is crucial for understanding local quantum information in gravity. Recent toy models have made progress by adding observers with clocks and imposing boost invariance, thereby enabling a rigorous von Neumann algebraic definition of generalized entropy. But they depend on auxiliary degrees of freedom and leave infinitely many diffeomorphisms unaddressed. It is natural to ask what happens when one tries to surmount these limitations.

I’ll show that including null translations lets us prove a version of the generalized second law beyond the semiclassical regime, with potential direct implications for black hole information. Then I’ll outline how the area degrees of freedom on a null surface define a quantum null time coordinate, and show how to use it to construct dressed operators invariant under all null diffeomorphisms (work in progress with Laurent Freidel.)

Speaker: Joshua Kirklin (Perimeter Institute for Theoretical Physics)

12:30 p.m. Lunch

2:00 p.m. Free Time

21 Topological Resummation in Quantum Gravity

The gravitational path integral remains one of the most elusive constructs in quantum gravity, particularly in regimes dominated by topological fluctuations. In this talk, I will present recent progress in Jackiw–Teitelboim (JT) gravity, where the sum over geometries can be made precise. We demonstrate that in a low-temperature regime where semiclassical approximations fail, the all-genus thermal partition function of JT gravity admits a resummation into an effective description on a single geometry with a nonlocal deformation. This construction gives formal and geometric realization to long-standing ideas from the 1980s on wormhole-induced nonlocality, linking them to ensemble interpretations and topological expansions. The resulting theory, defined on the disk with conical defect operators, captures the complete topological expansion through an emergent nonlocal interaction, providing a precise geometric window into strongly quantum gravitational dynamics.

Speaker: Sergio Hernandez-Cuenca (MIT)

22 Holographic pseudoentanglement and the complexity of the AdS/CFT dictionary

The quantum gravity in the lab' paradigm suggests that quantum computers might shed light on quantum gravity by simulating the CFT side of the AdS/CFT correspondence and mapping the results to the AdS side. This relies on the assumption that the duality map (thedictionary') is efficient to compute. In this talk, I will argue that the complexity of the AdS/CFT dictionary is surprisingly subtle: there might be cases in which one can efficiently apply operators to the CFT state (a task we call 'operator reconstruction') without being able to extract basic properties of the dual bulk state such as its geometry (which we call 'geometry reconstruction'), and vice versa. In order to reason about the complexity of geometry reconstruction we construct examples of holographic pseudoentanglement: that is, pairs of ensembles of states that obey the Ryu-Takayanagi formula for different geometries but which are nevertheless computationally indistinguishable. This result should be compared with existing evidence that operator reconstruction is generically easy in AdS/CFT. A useful analogy for the difference between these two tasks is quantum fully homomorphic encryption (FHE): this encrypts quantum states in such a way that no efficient adversary can learn properties of the state, but operators can be applied efficiently to the encrypted state. I will show that quantum FHE can separate the complexity of geometry reconstruction vs operator reconstruction, which raises the question whether FHE could be a useful lens through which to view AdS/CFT.

Speaker: Tamara Kohler (Stanford University)

3:30 p.m. Break

23 Von Neumann algebras in gravity (Vision Talk)

Speaker: Geoff Penington (University of California, Berkeley)

6:00 p.m. Movie Night - Arrival (2016)

Fri, June 27

24 Observers in quantum mechanics and quantum gravity (Vision Talk)

Speaker: Dan Harlow (MIT)

10:50 a.m. Break

25 Baby Universes and Holography: the Case of the Vanishing Universe

A number of recent arguments have suggested that baby universes in quantum gravity have a one-dimensional Hilbert space. I will provide a new argument, based on work with E. Gesteau, in favor of this conclusion. The argument makes use of a standard asymptotically AdS spacetime dual to a thermal state below the Hawking-Page transition. In particular, there is a low-energy, low-complexity causal wedge operator whose expectation value in the dual CFT is only consistent with a one-dimensional Hilbert space for baby universes.

Speaker: Netta Engelhardt (Massachusetts Institute of Technology (MIT))

26 Baby Universes and Holography II: Observer Complementarity

The notion of complementarity, first introduced in the context of the information paradox, posits that the experiences of two observers who cannot communicate need not match in quantum gravity. In the context of the previous talk, I will argue that the recent proposals for explicitly taking observers into account provide a way to describe semiclassical closed universes in holography, at the expense of a resort to complementarity. I will then discuss an analogous setup in the case of an evaporating black hole, and propose a set of general principles for black hole complementarity.

This talk is based on an ongoing collaboration with Netta Engelhardt and Daniel Harlow.

Speaker: Elliott Gesteau (Caltech, UCSB)

12:30 p.m. Lunch

2:00 p.m. Free Time

27 Does connected wedge imply distillable entanglement?

In holography, when two boundary subsystems have large mutual information, they are connected by their entanglement wedge. However, it remains mysterious whether these subsystems are EPR-like entangled. In this talk, I resolve this problem by finding bulk duals of one-shot distillable entanglement. Namely, I show that in one-shot scenarios: i) there is no distillable entanglement only by local operations at leading order in $G_N$, suggesting the absence of bipartite entanglement in a holographic mixed state, and ii) one-way LOCC-distillable entanglement is related to the entanglement wedge cross section, which is further dual to entanglement of formation. By demonstrating an explicit distillation protocol by holographic measurements, I conclude that a connected wedge does not necessarily imply finite distillable entanglement even when one-way LOCC is allowed. This talk is based on arXiv:2411.03426 [hep-th] and 2502.04437 [quant-ph].

Speaker: Takato Mori (Rikkyo University)

28 Canonical purifications revisited

I will use algebras to revisit and generalize the theory of canonical purifications, explain the general concept of "CRT sewing without gravity," and explain how this technology allows the influential-but-complicated "Araki-Yamagami theorem" from the '80s to be proved with 10x less work using a QI-motivated trick. Based on work with Caminiti and Capeccia.

Speaker: Johnathan Sorce (MIT)

29 On the reconstruction map in JT gravity

A key question in holography is how to reconstruct bulk operators in the holographic dual. It is especially interesting to reconstruct operators inside the black hole interior, but also especially difficult to do explicitly. Recently, an explicit form for the bulk-to-boundary holographic’ map was proposed in JT gravity, by Iliesiu, Levine, Lin, Maxfield, and Mezei, who also proposed and studied an explicitreconstruction’ map on operators. In this talk, I will discuss various pros and cons of their reconstruction map, and propose an alternative map with perhaps nicer properties.

Speaker: Chris Akers (University of Colorado Boulder)

4:00 p.m. Break